1. Field of the Invention
The present invention relates to a catalyst for polymerizing a cyclic olefin having a polar functional group and a polymerization method, and more particularly, to a catalyst system for polymerizing a cyclic olefin having a polar functional group, a polymerization method using the same, an olefin polymer produced by the method, and an optical anisotropic film comprising the olefin polymer.
2. Description of the Related Art
Among catalyst systems used in polymerization reactions, a homogeneous Ziegler-Natta catalyst system which generally has multiple active sites includes methylaluminoxane (MAO) as a cocatalyst to improve the reactivity of the catalyst. However, a large amount of the MAO should be used relative to the catalyst precursor, and thus an increase in production cost and the requirement of post-treatment arise.
With appearance of single active site catalysts such as metallocene catalysts, a perfluoroarylborate type non-coordination anion capable of providing single cation active species to a catalyst precursor, having low charge of −1 or −2 and easily achieving delocalization of charges has been used as a cocatalyst (Chem. Rev. 1988, Vol. 88, 1405-1421; Chem. Rev. 1993, Vol. 93, 927-942).
Such an anion is used in the form of a salt in combination with trityl causing an alkide or hydride removal reaction or dialkylammonium cation causing protonolysis. Exemplary borate cocatalyst compounds include [Ph3C][B(C6F5)4] and [PhNMe2H][B(C6F5)4].
In the polymerization reaction, the cation part of a cocatalyst reacts with a leaving group of a metal precursor to provide a cationic metal precursor and forms an ion pair with the anion part of the cocatalyst. The anion weakly coordinates to the metal and is easily exchanged with an olefin monomer, resulting in polymerization.
The ion pair acts as a catalyst active species, but is thermally and chemically unstable and sensitive to solvents, monomers, etc., and thus reduces the reactivity of a catalyst. In particular, in the case of a nitrogen containing cocatalyst compound, a neutral amine compound is produced during a catalyst active reaction and can strongly interact with a cationic organometallic catalyst, thereby resulting in a reduction of the catalytic activity. To avoid this problem, carbenium, oxonium and sulfonium cations can be used instead of the ammonium cation (EP Patent No. 0426,637).
Meanwhile, when cyclic olefins are polymerized using MAO or organoaluminium, in most cases, high polymerization activity is shown against a non-polar norbornene such as norbornene, alkylnorbornene and silylnorbornene, whereas significantly low polymerization activity is shown against a polar norbornene such as ester or acetyl norbornene (U.S. Pat. Nos. 5,468,819, 5,569,730, 5,912,313, 6,031,058 and 6,455,650).
Norbornene polymers which are composed of cyclic olefin monomers such as norbornenes exhibit much better properties than conventional olefin polymers, such as high transparency, heat resistance and chemical resistance, and have low birefringence and moisture absorption. Thus, they have various applications, e.g., optical components such as CDs, DVDs and POFs (plastic optical fibers), information and electronic components such as capacitor films and low-dielectrics, and medical components such as low-absorbent syringes, blister packagings, etc. Adhesion of polymers to inorganic materials such as silicon, silicon oxide, silicon nitride, alumina, copper, aluminium, gold, silver, platinum, titanium, nickel, tantalium, and chromium is often a critical factor in the reliability of the polymer for use as an electronic material. The introduction of functional groups into norbornene monomers enables control of chemical and physical properties of a resultant norbornene polymer. However, in this case, a problem of reduction in reactivity occurs.
That is, although catalyst systems for polymerizing cyclic olefins having polar functional groups can be prepared using various cocatalysts, the resulting catalysts are sensitive to monomers and deactivated or not used at high temperatures due to poor thermal stability. Thus, the polymerization yield, the molecular weight of the resulting polymers, and the amount of catalyst used are not at practical desired levels, as in the case of general olefins having polar functional groups. When an excess of catalyst is used, the resulting polymer is colored or its transparency is deteriorated.
Therefore, there is a demand for a novel catalyst system capable of producing a cyclic olefin polymer having polar functional groups from a small amount of catalyst which has thermal and chemical stability to solvents, monomers, moisture and oxygen by simultaneously and properly controlling a cocatalyst structure and a procatalyst structure.